Silica (SiO2) particles are commonly used as abrasive and/or thickeners in oral care compositions usually in the form of fumed silica or precipitated silica. One of the benefits of using silica is their low cost. However, silica has limited utility besides its abrasive and/or thickening effect. As a result, other active agents must be added to an oral care composition to provide a desired effect (e.g., adding an anti-bacterial agent to provide an anti-bacterial effect, adding tartar-control agents for tartar control). The need to add other active agents not only raises the possibility that the oral care composition will not meet regulatory burdens which can arise when the other active agents are used, but also increases the possibility that the oral care composition will not be desirable to the user of the composition (e.g. user sensitivity to the surfactant sodium lauryl sulfate (SLS), user aversion to the taste of a zinc compound, salty flavor and crystallization issues with current tartar-control agents etc.). Moreover, further problems may arise. For example, a common problem with the use of an anti-bacterial agent is the development of resistance by bacteria to the agent.
Core-shell structured colloidal particles have been known for several decades. The most famous example is the light-diffracting precious Opal which is formed slowly in several thousand years in natural environments. Its core-shell structures were discovered by electron microscope in 1960s. Various synthetic core-shell colloidal particles have been made since then. However, the synthesis of such core-shell materials is often complex, requiring multistep coating methodologies (See Kalele et al, “Nanoshell particles: synthesis, properties and applications”, current science, vol. 91,no. 8, 25 Oct. 2006). Therefore although the core-shell technology has been known for several decades, it has not yet been applied in the dentifrice industry, probably due to the high cost of making the CSS abrasive materials.
Therefore, there is still a need in the art for oral care compositions with multifunctional effects, but with a minimum of ingredients necessary to achieve the multifunctional effects. There is also still a need to develop additional anti-bacterial agents and tartar control agents suitable for use in oral care compositions.